Matthew Holehouse is a political correspondent at the Daily and Sunday Telegraph. He can be emailed at matthew.holehouse@telegraph.co.uk.

Will 2015 be like 1983? Cameron's polling turnaround challenge

Polling forecasts, 1983 to 2010. The beginnings of the lines mark the polling forecast two years before the election. The dot in the middle marks one year til election day, and the dot at the end is the final outcome.

How far from outright victory in 2015 is David Cameron? It’s now a year and ten months until the election, and the Conservative Party has a spring in its step.

The economy's up and Ed Miliband is under fire. Such is the confidence that the original target list of 40 winnable seats into which CCHQ will pour resources is now regarded as under-ambitious; there are high hopes for the newly-selected candidates for the tough seats of Westminster North (Labour majority 2,126), Taunton Deane (Lib Dem majority 3,993) and Tooting (Labour majority 2,524), amongst others.

Labour strategists, meanwhile, ask you to point to which seats they could possibly lose after the nadir of 2010 – and then point to plenty they could win. Today’s poll lead of seven points (Con 32, Lab 39, LD, 10, Ukip 12) is forecast to make Ed Miliband Prime Minister with a majority of 84.

We calculate that a poll lead of 6 and a half for the Tories, based on a universal swing, would deliver Cameron a majority of 2. An extra half per cent should give him a working majority of 22. (You can make predictions on the Electoral Calculus site here.)

So Cameron, if he wants that majority, needs to turn a 7-point deficit into a 7-point lead. Can it be done?

Electoral Calculus have produced a graphic (above) for us which charts the polling trajectories of the last seven general elections.

Labour’s share of the vote is plotted along the y-axis; the Tories’ along the x-axis. The red, yellow and blue shaded areas show which party forms the government, according to those shares of the vote, while the grey no-man’s land in the middle is a hung parliament.

The lines represent the polling in the run-up to each election since 1983. The start of the line marks the forecast outcome, based on polling two years before the election. The mid-point is that same forecast one year before the election. The dot on the end is the actual result.

For example: We see then that in the spring of 1981, Mrs Thatcher was not far off where Mr Cameron – the grey circle on the map – sits now, with Ipsos Mori giving a 6.6 per cent lead to Michael Foot and a forecast Labour government (Con 30.9, Lab 37.5, Lib 29.6). By 1983, a poll surge on the back of the Falklands War resulted in a Tory lead of 14.8 points (Con 42.4, Lab 27.6, Lib 25.4) and granted Mrs Thatcher a majority of 144.

We see then how successive Tory governments have clawed their way back from polls that forecast defeat, securing double-digit turnarounds in two years. In the 1987 election, a tie in the polls became a 12 point lead for the Tories.

And in the long campaign of 1990-92, a 14-point deficit for Major (Con 35.4, Lab 49.1, Lib 8.8) became an 8-point lead (Con 42.8, Lab 35.2, Lib 18.3) – an effective turnaround of 22 points that saw him keep Neil Kinnock from Downing Street.

John Major in 1997 and Gordon Brown in 2010 both saw their polling pick up in the two years before the election, albeit by not enough to save their Governments. Mr Major closed the gap from 28.6 points (Blair was polling at an eye-watering 55 in the spring of 1995) to 12.5 points, a gap of 16; while Mr Brown, for all his woes, still managed to cut the poll deficit from 12.4 points to 5.4, denying David Cameron a majority.

In only two cases – Blair in 2001 and 2005 – did the Government poll worse on election day than it did mid-term.

So there is a clear precedent for a sitting Prime Minister to pull off, as Cameron must, a 14-point turnaround in two years and remain in office.

But what the graph also underlines is just how poor recent Tory election performances have been. The polls barely shifted in 2003-05, but that shift of less than one point was away from the Tories. And in 2009, David Cameron enjoyed a 13-point lead and was on course for a majority. Some dared to predict a landslide bigger than Blair's. We know what happened next.